This invention relates to the field of three-dimensionally contoured packing sheets molded to substantially finished form from resilient material such as fibrous pulp or foam plastic, for packing in a shipping case or other container a stack of at least two directly superimposed layers of a plurality of elongated fragile objects, such as cylindrical fluorescent light tubes.
Molded packing sheets have been used with great success for many years to pack elongated fluorescent light tubes in shipping cases. The purpose of the packing sheets is to safeguard the tubes against breakage, by protecting them from mutual contact in the shipping case, and also to facilitate loading a stack of two or more layers of the tubes into the shipping case. The sheets are made of resilient material, such as molded fibrous pulp, which imparts cushioning characteristics to further protect the fragile tubes against breakage when a shipping case of the same encounters rough handling.
A typical molded pulp packing sheet, of the single layer type over which the present invention is a new and useful improvement, is disclosed in Chadbourne U.S. Pat. No. Des. 249,638 issued September 1978. This consists of a packing sheet molded to substantially finished form from fibrous pulp material which is three dimensionally contoured to provide upwardly directed contours including longitudinally spaced apart tube cradling surfaces for each tube and longitudinally extending narrow tube separating ribs for a plurality of tubes in an upper layer, and downwardly directed contours including a series of flat support surfaces to hold the rest of the sheet elevated thereabove to facilitate drying of the damp sheet during manufacture. See also in this regard Emery U.S. Pat. No. 2,984,345 issued May 1961.
One problem with light tube packing sheets of this general type occurs during the process of loading a stack of several layers of packed light tubes into a shipping case, the problem being that one layer of packed tubes tends to shift laterally with respect to a vertically adjacent layer of packed tubes in the stack, and the resulting mis-alignment makes it difficult to load the stack into the shipping case.
This problem is an old one, which has been recognized since the 1940's, as explained in Shepard U.S. Pat. No. 2,564,729 issued August 1951, and also in Shepard U.S. Pat. Nos. Des. 143,042 issued November 1945 and 2,568,769 issued September 1951. The Shepard '729 patent utilizes a packing sheet of the "double layer" type which folds back upon itself to provide both upper and lower protection for the ends of the light tubes, and solves the lateral shifting problem by means of cooperating raised formations and recessed formations in a "vertical" stack in which the tubes are positioned vertically directly one above the other. The other two Shepard patents utilize a packing sheet of the "single layer" type which does not fold back upon itself, and solve the lateral shifting problem by means of centrally located downribs which fit between adjacent tubes in the next lower layer but in a "staggered" stack in which tubes are horizontally offset in alternate rows.
While the Shepard patents disclose downwardly contoured means to prevent lateral shifting of one packed layer of tubes with respect to the packed layer of tubes immediately therebelow in the stack, they do not disclose a means of preventing lateral shifting in a "single layer" packing sheet of the general type disclosed in the aforesaid Chadbourne patent, for use in a so-called "vertical" stack of light tubes.
Thus, the problem heretofore unresolved by the prior art is the use of a single layer type packing sheet which includes means to prevent lateral shifting of one packed layer of light tubes with respect to an adjacent packed layer of tubes in a vertical as opposed to a staggered stack of tubes.